Outer surfaces of piston rings are often coated to improve performance characteristics of the rings, e.g., by altering frictional properties or wear characteristics of the surfaces. Some coatings, e.g., deposition coatings such as physical or chemical vapor deposition coatings, may generally improve break-in characteristics of the rings. However, deposition coatings may also suffer from disadvantages in wear life, and therefore rings employing such coatings may need to be replaced relatively more frequently. By contrast, other types of coatings that offer relatively better wear life and durability than deposition coatings may not break in as smoothly.
As such, piston ring manufacturers typically must generally accept certain disadvantages in performance depending upon which of the above coatings are selected. Moreover, efforts to limit the above disadvantages by combining coatings have been unsuccessful. For example, it has been difficult to obtain an adequate bond strength between different coatings, resulting in cracks, chips, or other failures in the applied coatings.
Accordingly, there is a need for an improved piston ring that addresses the inherent disadvantages of certain coating types, while allowing for a commercially practical method of application in a mass manufacturing environment.